OM humus1º minerals clays

OM, clay, ions Transformations:

runoff

leaching

Rain, OM

capillary rise

Four processes:

• Additions

• Losses

• Translocations

• Transformations

Influence of climate on Carbonate Layer Depth

i.e., near surface

Depth

Effect of Climate on Soil Formation

limestone dry climate

40cm

A

R

limestone wet climate

60cm

A

Bw

Cr

note depths of these profiles

T

ppt

Organisms / Climate influences on soil formation

Feb 18, 2002

Effect of Vegetation on SOM

Grass/Agric Land

Deciduous Forest

Coniferous Forest

Nutrient content of OM residue

OM decomposition

O horizon present

High High Low

Rapid Rapid Slow

No Seasonal Yes

SOM = soil organic matter

Blocky structure

Unweathered loess

Organic matter

CaCO3

Time

Grassland

Time

Temperate Deciduous Forest

Organic layer

Leached zone

Unweathered bedrock

Weathered PM Clays, oxides

Effect of Vegetation on Development

Soil Samples!

Time

Temperate Deciduous Forest

Organic layer

Leached zone

Unweathered bedrock

Weathered PM Clays, oxides

Effect of Vegetation on Development

Ultisol Sample!

Blocky structure

Unweathered loess

Organic matter

CaCO3

Time

Grassland

Effect of Vegetation on Development

Meadow Soil Sample!

Trinity Alps Wilderness AreaNorthern California

Topography as an Influence on Soil Formation

• Relief

• Aspect

• Elevation

(steep vs. flat)

(N,S,E,W)

(link to climate, organisms)

Landscape positions

Figure 2.13 Brady & Weil

Footslope

Toeslope

Effect of topography on soil formation

Summit

Backslope

Toeslope

Effect of Topography on Soils

Position Summit Shoulder Backslope Footslope Toeslope

% OC in

A horizon

Thickness of A

(cm)

Texture of A

4.01.5

lowest3.0 4.5

5.5

highest

156

lowest10 18

25

highest

si l l si lsi c lMost clay

si c lMost clay

E. Colorado; grassland; limestone

pH 7.0 7.2

Effect of time on soil development

Very mature

MatureYoungParent material

1m >1m 15mC C

A

C

A

Bw

C

A

E

Bt

Effect of time on soil development

Modern floodplain

Higher terraces

10cm

80cm

Time

A

C

A

Bt1

C

Bt2

• both formed in alluvium from mixed sources • similar topography

Effect of Time on Soils

Soil age, development

Immature (young)

Mature (old)

Mineral status

Fertility

Amount of clay

Primary: quartz,

feldspar, etc.

Secondary: smectites, illite, etc.

low

low high

high

Factors That Retard Soil Development

• Low rainfall and RH• Cold temperatures• High water table• Parent materials that are mostly quartz• Very high clay content• Presence of substances toxic to plants• Very steep slopes erosion• Disturbance frequency – e.g. fire

Soil Orders Study Guide

Saved as a separate file on-line